Ammonium nitrate explosive composition



United States Patent 2,992,912 AMMONIUM NITRATE EXPLOSIVE COMPOSITIONJoseph R. Hradel, Mount Pleasant, Mich., and Harold E. Staadt, Tulsa,Okla, assignors to The Dow Chemical Company, Midland, Mich, acorporation of Delaware No Drawing. Filed Jan. 5, 1959, Ser. No. 784,8674 Claims. ('CI. 52-14) This invention relates to an improved ammoniumnitrate explosive composition and more particularly concerns anammoniacal ammonium nitrate explosive composition containing carbon as asensitizer. It has been a desideratum in the explosives art to formulateand compound explosive compositions which may be handled and transportedwith relative safety yet reliably and effectively detonated. To fillthis need various ammonium nitrate explosive compositions have beenproposed but these have generally contained materials that are quiteshock sensitive or the compositions have required boosters such asgelatin dynamite spaced throughout a large load to insure goodprovocation,

It is an object of the present invention to provide an ammonium nitrateexplosive composition which may be safely handled and transported withlittle danger of shock initiation yet may be detonated eifectively by ashaped charge using the Monroe jet principle. 7

It is another object of the invention to provide an ammonium nitrateexplosive composition of moderate shock sensitivity which yet uponproper initiation produces a detonation of useful magnitude and force.

Another object of the invention is to provide an ammonium nitrateexplosive composition in the form of a paste or slurry whereby a chargeof the composition upon being loaded into a rigid or flexible container,or directly into a bore hole, contains a minimum of void spaces withinthe charge.

Another object of the invention is to provide an ammonium nitrateexplosive composition containing a sensitizer which is not adverselyaffected by moisture during storage of the composition.

An additional object of the invention is to provide an ammonium nitrateexplosive composition containing carbon as a sensitize'r.

A still further object of the invention is to provide a low costammonium nitrate explosive composition which is adapted to be readilycompounded near the point of use.

Other objects and advantages of the invention will become apparent toone skilled in the art upon becoming familiar with the followingdescription and claims.

These and other objects are attained upon admixing ammonium nitrate,itself cap insensitive, with a carbon sensitizer and with 'an ammoniacalsolution of ammonium nitrate in proportions hereinafter more fullydescribed and further illustrated by examples of the invention. Allproportions herein given in percent are to be understood as percent byweight unless otherwise indicated.

The composition of the invention may be compounded with fertilizer gradeas well as explosive grade ammonium nitrate. While the explosive gradematerial tends to detonate with slightly greater force on an equalWeight basis it is generally more economical to make up for this byusing a slightly greater amount of fertilizer grade ammonium nitrate.

Fertilizer grade ammonium nitrate generally contains various additivesor fine particulate coatings inhibiting caking and promotingfree-flowing characteristics of the material. Ammonium nitrate asreferred to herein is defined as ammonium nitrate containing up to 3percent of various additives such as wax, diatomaceous earth and chalk,in addition to a moisture content-ranging up to about 1% percent, eitherthe granular or prilled form of the nitrate salt are satisfactory.

To avoid making cap sensitive mixtures the composition is best preparedfrom ammonium nitrate having particle sizes mainly in the range of 8 to100 mesh, fines passing 100 to 200 mesh tending to increase thesensitivity of the mixture. An example of a satisfactory granularammonium nitrate readily obtained commercially has the following sieveanalysis:

Table I Number Number Percent of sieve 1 of sieve re retained passedtamed on 12 0.3 12 20 34. 4 20 30 16. 4 30 40 13.4 40 60 14. 4 60 8. 480 100 1.9 100 200 6. 4 200 Pan 4. 4

Table 11 Number Number of sieve of sieve Percent passed retainedretained 6 0 6 10 56 10 12 24 12 14 9 14 20 9 20 35 2 35 Pan Tr.

The above examples are not intended to limitative but indicative of thenature of commercially available am-, monium nitrate.

Carbon in the form of finely ground coke, charcoal or coal as well ascarbon black or lamp black is suitable for use in compounding thecomposition of the invention. Fine particulate carbon passing a 325 meshsieve is to be preferred though carbon having particle sizes up to thatretained on a 60 mesh sieve may be used if desired. Coarse particulatecarbon tends to react slower during a detonation and is thus lessefliciently use.

A suitable ammoniacal solution of ammonium nitrate is Divers liquidwhich is a saturated or nearly saturated anhydrous solution of ammoniumnitrate in liquid ammonia containing generally about 60 to 80 percent ofammonium nitrate. A similar ammom'acal solution of ammonium nitratecontaining in addition up to 15 percent of water is referred to hereinas an ammoniacal solution of ammonium nitrate. Such aqueous ammoniacalsolutions are commercially available at lower cost and are easier tohandle than the anhydrous Divers liquid because of the reduced vaporpressure of the ammonia therein in the presence of water. As an example,a solution consisting of 60 percent of ammonium nitrate, 34 percent ofliquid ammonia and 6 percent of water is commercially available.

The hereinabove described components of the explosive mixture of theinvention may be combined in various proportions ranging from 6 topercent of solid particulate ammonium nitrate, from 0.5 to 20 percent offinely divided carbon and from about 3 to 87 percent of an ammoniacalsolution of ammonium nitrate containing up to 30 percent of water andsubstantially saturated with respect to ammonium nitrate. It is to beunderstood that while compositions in this range, will, under roomtemperature conditions, contain both dissolved ammonium nitrate andsolid phase particulate ammonium nitrate in the proportions described,the relative amount of ammonium nitrate in each phase is determined bythe temperature and pressure of the mixture under equilibriumconditions. At higher temperatures under a constant pressure more solidparticulate ammonium nitrate will be taken up by the solution and atlower temperatures a lesser amount. For this reason the invention hasbeen defined above with respect to mixtures equilibrated at roomtemperature and under atmospheric pressure.

In another manner of defining the explosive composition of theinvention, that is, in terms of the individual molecular or elementalspecies from which the composition may be prepared if desired, theproportions range from 60 to about 97 percent of ammonium nitrate total,from 0.5 to 20 percent of finely divided carbon, from 1 to 30 percent ofammonia and up to 3 percent of water.

Mixtures of the invention containing less than about 18 to 20 percent ofliquid solution phase are generally in the form of a lumpy paste and areadvantageously loaded into accessible bore holes or placed in suitablecontainers which may be charged into a bore hole as in mining orquarrying operations.

Mixtures of the invention containing more than about 20 percent of theliquid solution phase are to be preferred for pumping into a bore holeas a slurry and are especially advantageously used in loading anelongated horizontal or upwardly sloping bore hole.

If desired, the explosive composition of the invention may be thickenedupon admixing therewith from about 0.12 to 5 percent, based on theWeight of the liquid phase, of a thickening agent such as methyilcellulose or gum karaya. Other suitable thickening agents arecarboxymethyl cellulose, kava-kava gum, guar gum, accroides gum, locustbean gum, gum tragacanth, balsam tolu natural, gum bezoin Sumatra, Irishmoss, Iceland moss and Separan NP-IO (a high molecular weightpolyacrylarnide). The effects of various thickening agents on theviscosity respectively, of Divers liquid and of an aqueous ammoniacalsolution also known as Spensol D, a trademarked product, and containing60'peroent of ammonium nitrate, 34 percent of ammonia and 6 percent ofwater were determined and the results are listed in Table HI.

Table III Viscosity of ammoniacal solution after addition Weight ofthickener (cps) Thickener percent of thickener Diver's Spensol D liquid5 100, 000 100, 000 Guar gum 5 41 100, 000 Kava kava gum 5 450 Accroidesgum 120 1100111350 bean gum 13 o 100, 000 Balsam tolu natural gum- 20Irish moss 60 Iceland moss- 42 Separan NP 10. 140 Methocel HG...-. Do 1977 315 95, 000 18 28 5 142 1 395 5 84, 000 4, 000

' In preparing and detonating the composition of the invention theingredients of the composition are mixed together in small quantities asby kneading in a plastic bag or in larger quantities as with amechanical agitator or paddle mixer. A load or charge of the so preparedmixture is placed in the desired location, usually in the confinement ofa bore hole. A shaped charge, such as a commercially available jetperforator containing a charge of RDX is armed with a suitable initiatorsuch as a No. 8 blasting cap and placed next to the load. The shapedcharge is oriented with respect to the explosive load so that the firingaccess is directed toward the load, preferably its mid-point. Theelectrical lead for the blasting cap is rigged to a time controlledfiring mechanism or run to a remote control device and, if desired, asand or gravel tamp is placed over the load and initiator. The load isthen fired upon setting off the blasting cap and shaped charge.

To demonstrate the properties of the ammonium nitrate explosive mixtureof the invention various embodiments of the invention were compared andtested. In each test a 10 pound quantity of explosive mixture wasformulated of a particulated fertilizer grade of ammonium nitrate,finely divided carbon black and ammonia, or of a particulated fertilizergrade ammonium nitrate, finely divided carbon black and an aqueousammoniacal solution of ammonium nitrate known as Spensol D in theproportions and amount shown hereinbelow in Table IV. The individualproportions were in each case mixed in a separate polyethylene plasticbag of suflicient size 'to readily hold the quantity prepared. Thevarious components of the mixture were weighed into the bag, the bagclosed and the contents mixed together by kneading the bag with thehands. The fertilizer grade of ammonium ntirate contained about 0.7percent of wax, 1 percent of diatomaceous earth and 0.3 percent ofchalk. The particle size of the ammonium nitrate was such that 94percent by weight of the particles passed a 20 mesh sieve and percent byweight were retained on a mesh sieve. The carbon was in the form ofcarbon black.

The prepared mixtures were loaded into individual shallow bore holesdrilled in clay soil and having a diameter of 4 inches and depth ofabout 4 feet. Successive bore holes were spaced about 20 feet apart. Theloading of each hole was accomplished by first placing an initiator inthe form of a shaped charge armed with a blasting cap in the bottom ofthe hole and running the lead wires from the blasting cap to a firingcontrol switch. Each shaped charge used was positioned with the jet endor firm'g axis facing upwardly. The explosive mixtures, contained in theplastic bags in which they were mixed, were dumped into respective testholes, the bags in each case deforming over the initiator. Sand was usedas a tamp, the hole being filled from the bag to ground level 'withsand. Detonation of the mixture was attempted by closing the firingswitch thus setting off the initiator at the bottom of the hole. Themagnitudes of the detonations obtained were determined by measuring thesize of the crater produced. While the crater size alone is notindicative of the amount of earch formation that is broken up orloosened, it does give an indication of. the work potential of themixture detonated. The crater size herein reported shows how muchmaterial was thrown sufiiciently so as not to fall back over the testhole. Test conditions and results are summarized in Table IV.

In order to compare the composition of the invention with conventionalexplosives varied amounts of 60 percent dynamite each with a No. 8electric blasting cap therefore were placed in shallow test holes 4 feetdeep, tamped with sand and detonated. 5 pounds of dynamite so loaded anddetonated produced a crater 5 feet in diameter and 1.5 feet deep; 10pounds of dynamite produced a crater 8 feet in diameter and 1 foot deep;while 25 pounds of dynamite produced a crater 11 feet in dimeter and 5feet deep.

n In another test series additional embodiments of the invention werecompounded. Each mixture was used to entirely fill a 3 inch x 12 inchsteel pipe nipple which was capped on both ends and laid on the ground.The change was initiated by a shaped charge containing 3.25 oz. of RDXwhich Was positioned at one end of the nipple so as to tirelongitudinally into the nipple. In one such test the steel pipe nipplewas heated by electrical resistance heating elements and the contents ofthe nipple subjected to hydrolic pressure.

The compositions tested and the results obtained are summarized in TableV.

Table IV Composition Initiator Crater dfinensions,

Gum Weight Test No. Kaof load, Weight raya lbs. Blasting RDX in Diam-FGAN NHa S.D. cap shaped eter Depth charge, oz.

89 6 1O 8 EB O 1 8 2. 94 1 8 EBO 1 5 5 81 4 l0 8 EBO 1 6 2 94 1 10 8E130 l 9 1 84 1 10 8 EBO 1 9 1 78 2 l0 8 EBO 1 9 1 87 3 10 8 EBO 1 9.5 1. 5 80 1O 8 EBO 1 8 6 75 5 10 8 EBO 1 6 Heaved. 85 13 34 10 8 EBO 3.25 7 4 85 10 y 10 8 EBO 3. 25 7 4 90 s i 10 8 E30 3. 25 s 4. a 97 2 5410 8 EBO 3. 25 8 4 80 10 34 10 8 EBO 3. 25 10 5 85 5 V 10 8 EBC 3. 25 126 93 4 10 8 E130 3. 25 12 6 96 2 x 10 8 EBC 3. 25 12 6 84 3 $4 10 8 EEC3.25 10 5 70 15 $4 10 8 EBO 3. 25 8 6 73 $4 10 8 EBO 3. 10 6EGAN-fertilizer grade ammonium. S.D.Spensol D RDX-trimethyienetrinitramme.

1 Percent based on weight of liquid phase at room temperature.

a commercial aqueous ammoniacal solution of ammonium nitrate.

The results show that a composition of the invention containing from 60to 80 percent of ammonium nitrate is efiectively detonated by a shapedcharge under the conditions of the test.

The compositions of the invention possess the advantage that they may beslurried in an additional amount of an ammoniacal solution of ammoniumnitrate and pumped into a bore hole and there allowed to settle out toform a detonable composition.

What is claimed is:

1. An ammonium nitrate explosive composition consisting essentially ofparticulate ammonium nitrate in admixture with from 0.5 to 20 percent byweight of finely divided carbon and with an ammoniacal solution which issubstantially saturated with respect to ammonium nitrate, saidammoniacal solution containing a proportion of ammonia equivalent tofrom 1 to percent by weight of the total weight of the admixture, saidammoniacal solution further containing up to 30 percent by weight ofwater, but the said water not exceeding 3 percent of 30 percent byweight of water based on the weight of the ammoniacal solution, the saidWater not exceeding 3 percent by weight of the total weight of theadmixture, said ammoniacal solution having a proportion of ammoniaequivalent to from about 5 to 15 percent by weight of the total weightof the admixture and said admixture containing a combined total in allphases of at least percent by weight of ammonium nitrate.

4. The explosive composition as in claim 1 admixed with from 0.12 to 5weight percent of gum karaya whereby the viscosity of the saidammoniacal solution is increased.

References Cited in the file of this patent UNITED STATES PATENTS2,168,562 Davis Aug. 2, 1939 2,393,594 Davis Jan. 29, 1946 2,703,528 Leeet a1. Mar. 8, 1955 2,836,484 Streng et a1. May 27, 1958 2,860,041Griflith et a1. Nov. 11, 1958

1. AN AMMONIUM NITRATE EXPLOSIVE COMPOSITION CONSISTING ESSENTIALLY OFPARTICULATE AMMONIUM NITRATE IN ADMIXTURE WITH FROM 0.5 TO 20 PERCENT BYWEIGHT OF FINELY DIVIDED CARBON AND WITH AN AMMONIACAL SOLUTION WHICH ISSUBSTANNTIALLY SATURATED WITH RESPECT TO AMMONIUM NITRATE, SAIDAMMONIACAL SOLUTION CONTAINING A PROPORTION OF AMMONIA EQUIVALENT TOFROM 1 TO 30 PERCENT BY WEIGHT OF THE TOTAL WEIGHT OF THE ADMIXTURE,SAID AMMONIACAL SOLUTION FURTHER CONTAINING UP TO 30 PERCENT BY WEIGHTOF WATER, BUT THE SAID WATER NOT EXCEEDING 3 PERCENT OF THE TOTAL WEIGHTOF THE ADMIXTURE, AND SAID ADMIXTURE CONTAINING A COMBINED TOTAL IN ALLPHASES OF AT LEAST 60 PERCENT BY WEIGHT OF AMMONIUM NITRATE.